Anti-reflection (AR) coatings are known in the art. SFO (solar float) and MM (matte-matte) glass, for example, have been coated using sol-gel processes to provide anti-reflective optics. However, SFO and MM glass developed using known sol-gel processes could be improved by providing better resistance to salt fogs and/or other forms of moisture that could corrode the coatings and cause them to degrade in anti-reflective performance and/or create undesirable visible appearances.
A salt fog test chamber may include steam vapor of NaOH and NaCl with a chamber temperature of 35° C. and pressure of 16 psi. Inability to sufficiently resist corrosion in salt fog environments simulated using a salt fog test chamber such as this may limit the application of anti-reflection (AR) glass used in some environments such as, for example, environments near oceans, with high mineral moisture, etc. For instance, a thin AR film can be easily removed after a salt fog test, e.g., after being structurally attacked in a manner that damages the adhesive strength between thin film and glass or other substrate that supports the coating.
It also is believed that alkali ions are preferentially leached from multiple components silica glasses with alkali oxides. The failure mechanism noted above thus could be attributed to the unsymmetrical glass, e.g., resulting from the attacks of sodium ions (Na+) migrating from the glass bulk to the surface of the AR thin film. Some Na+ ions in a salt fog solution could also provide a source to attack the AR thin film.
During salt fog testing processes, Na+ ions from the glass substrate may diffuse into the AR coating layer, and consequently the properties of AR thin film may be changed. In some instances, there may be a layer of reduced sodium concentration and increased hydrogen amount near the glass-solution interface. When alkali ions are leached from the glass, it may provide a space that can allow water molecules to penetrate into the coating.
A hydrated layer could then be generated, especially in less durable glass. A more open structure in the hydrated layer of or on the glass surface may result in a faster transfer of ions from the glass, and a swell structure may also be found on a hydrated layer. Furthermore, hydroxyl groups produced by ion exchange between Na+ and H2O may boost the hydrolysis of the siloxane bond and result in fatigue-type damage to the AR thin film.
Thus, it will be appreciated that there may be instances where it would be desirable to improve the chemical stability of AR thin films in potentially corrosive environments, e.g., as simulated by a salt fog chamber.
It is believed that, prior to the present disclosure, there was no reason to expect that the inclusion of hybrid alkoxides in an AR coating would lead to good durability for that coating. In fact, those skilled in the art might expect that AR coatings that include hybrid alkoxides would not be very strong and thus would not provide good durability.
This expectation stems from the belief that one might expect potential failure locations to be present at discontinuities in the coating, and the inclusion of hybrid alkoxides logically would involve a higher than usual number of potential failure locations, e.g., because of the structure of the alkoxides themselves as exacerbated by the hybrid materials included in the coating.
Yet despite these preexisting expectations, the present application relates to the inclusion of hybrid alkoxides in the AR coating of certain example embodiments, which surprisingly and unexpectedly leads to improved durability of the coating. More particularly, it is believed that the specific bonding energies of the materials may promote a sort of “self-healing” coating in ways that would not have been expected and that are surprising and unexpected.
In certain example embodiments, there is provided a method of making a coated article comprising an anti-reflection coating supported by a glass substrate. The method includes depositing on the glass substrate at least a portion of a solution comprising at least one hybrid alkoxide selected from the group consisting of Si(OR)4—Al(s-OBu)3, Si(OR)4—B(OBu)3 and Si(OR)4 and Zr(OBu)4, where R is a CH2CH3 group, s-OBu is sec-butoxide and OBu is n-butoxide, respectively, optionally with a silicon nanoparticle and a siloxane, to form a substantially uniform coating. The solution is cured and/or allowed to cure, in making the anti-reflection coating.
In certain example embodiments, there is provided a coated article comprising an anti-reflection coating supported by a glass substrate. The anti-reflection coating comprises a reaction product of a hydrolysis and/or a condensation reaction of at least one hybrid alkoxide selected from the group consisting of Si(OR)4—Al(s-OBu)3, Si(OR)4—B(OBu)3 and Si(OR)4 and Zr(OBu)4, where R is a CH2CH3 group, s-OBu is sec-butoxide and OBu is n-butoxide. The anti-reflection coating has a refractive index less than 1.5.